1. Field of the Invention
The present invention relates to a method and apparatus for driving a display device such as liquid crystal display, plasma display, EL display and LED display.
2. Description of the Prior Art
Hitherto, for example, for gradation display by a liquid crystal display device of active matrix driving system, analog signals are applied as the display data corresponding to each pixel disposed in matrix on a display panel, and the control voltage of the display panel is varied depending on the magnitude of the analog signal, thereby achieving gradation display.
In other method, digital signals are given as the display data, and the analog voltage corresponding to input digital value is selected, and the selected analog voltage is used as the control voltage of the display panel for gradation display.
In a liquid crystal display apparatus of simple matrix driving system, a frame thinning method is employed for gradation display. In this method, plural display frame periods are determined as one cycle, and depending on the gradation to be displayed, the number of display frames for ON driving of the pixels in the cycle and the number of display frames for OFF driving of the pixels are variably set.
In the case of plural gradation displays by a large liquid crystal display device of 10 inches or larger size by using such conventional method, since the capacity of the electrode becomes large because of the large size of the display panel, when an analog signal is fed as display data, it becomes difficult to drive the electrode by transmitting the analog voltage at high speed.
Or when entering digital value as display data, it is necessary to generate the analog voltage by the number of the digital values, and prepare the changeover circuits for selecting the voltages by the number of pixels per line to be arranged on the display panel, which results in the increase of the circuit scale.
Furthermore, in the case of plural gradation displays by the frame thinning method, in the liquid crystal display device of simple matrix driving system, there is no problem because the response speed is slow, but in the liquid crystal display device of active matrix driving system, the response speed is high, and the flicker is very obvious, and the display grade is extremely lowered.